1. Field of the Invention
The present invention relates to a novel fluorovinyl ether. More particularly, it relates to a fluorovinyl ether which is a useful modifier for a polymer comprising an ethylenically unsaturated compound.
2. Description of the Related Art
Copolymerization of two or more fluoroolefins or a fluoroolefin with a fluorine-free olefin gives various kinds of copolymers from a resin to an elastomer according to a composition of the monomers. The copolymer comprising the fluoroolefin can be molded to produce mechanical parts (e.g. O-rings, flange seals, gaskets, diaphragms, liners, etc.) and particularly useful in cases where special resistances to heat and corrosive fluids are required.
As fluorine-containing elastomers, known are copolymers of vinylidene fluoride/hexafluoropropylene, tetrafluoroethylene/propylene, tetrafluoroethylene/perfluoro(alkyl vinyl ether), vinylidene fluoride/perfluoro(alkyl vinyl ether) and the like.
These fluorine-containing elastomeric copolymers has insufficient properties at low temperature and are hardly used at low temperature, although they are superior to hydrocarbon type elastomers in heat resistance, oil resistance chemical resistance and so on.
To overcome such drawbacks of the fluorine-containing elastomers, a blending method such as co-cross linking with a silicone rubber has been attempted. However, to improve the low temperature properties, the blend should comprise the-silicone rubber as a main component so that the characteristics of the fluorine-containing elastomer are suppressed. Alternatively, addition of a certain kind of plasticizer to the fluorine-containing elastomer is proposed. However, under some conditions, the plasticizer is separated. Therefore, the intended elastomer having good resistance to low temperature has not been provided.
To improve the low temperature properties of the fluorine-containing elastomer by introduction of ether linkages in its backbone chain, ionic polymerization of hexafluoropropylene oxide, radical polymerization of a fluorine-containing ketone-and condensation of fluorine-containing polyether are investigated. However, no practical elastomer has been produced by these methods.
Introduction of an ether linkage in a side chain of the fluorine-containing elastomer has been studied to improve the low temperature properties. For example, copolymerization of vinylidene fluoride or tetrafluoroethylene with a fluoro(alkyl vinyl ether) of the formula: EQU CF.sub.2 =CFOR.sub.f
wherein R.sub.f is a perfluoroalkyl group such as --CF.sub.3, --C.sub.2 F.sub.5 or --C.sub.3 F.sub.7 gives an elastomeric copolymer. However, a glass transition temperature (T.sub.g) of the copolymer cannot be sufficiently lowered even when a content of the fluoro(alkyl vinyl ether) is increased as high as possible.
Among the fluorovinyl ethers, a fluorovinyl ether having plural ether linkages in a molecule can effectively improve the low temperature properties of the fluorine-containing elastomer. By copolymerizing the fluorovinyl ether having plural ether linkages with the fluorine-free olefin or the fluoroolefin, a fluoroelastomer having low temperature properties to some extent is produced (cf. Japanese Patent Kokai Publication No. 18710/1982 and Japanese Patent Publication Nos. 50486/1986 and 57324/1987). However, none of them has satisfactory low temperature properties.